An internal combustion (IC) engine may include an exhaust gas recirculation (EGR) system for controlling the generation of undesirable pollutant gases and particulate matter in the operation of IC engines. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the IC engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the IC engine.
An IC engine may also include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel and air mixture.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is typically removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve directly from the exhaust manifold. The percentage of the total exhaust flow which is diverted for introduction into the intake manifold of an internal combustion engine is known as the EGR rate of the engine.
EGR has proven effective in reducting NOx emissions from modern diesel engines. EGR rates of up to 50% may be needed for tier 4 engines if selective catalytic reduction (SCR) is to be eliminated. Variable geometry turbochargers may be needed to increase exhaust pressures so as to drive exhaust gases into the intake system of high pressure loop EGR systems. The impact of the higher exhaust pressures significantly increases pumping losses, and raises peak firing pressures. It is also difficult to drive EGR levels high enough to meet NOx regulations without aftertreatment. Cooling loads also increase significantly with high EGR levels.
What is needed in the art is an EGR system that can operate at high EGR levels in a high pressure loop EGR system.